Acetolactate synthase (ALS) inhibitors are widely used for POST control ofsedges in turfgrass. A suspected resistant (R) biotype of annual sedge wascollected from a bermudagrass turf in Georgia with a history of exclusiveuse of halosulfuron. Research was conducted to evaluate the resistance levelof this biotype to halosulfuron, efficacy of ALS-inhibiting herbicides andother mechanisms of action for control, and the molecular and physiologicalbasis for resistance. In greenhouse experiments, the halosulfuron raterequired to reduce shoot biomass 50% in comparison with the nontreated at 8wk after treatment (WAT) were 8 and > 1,120 g ai ha−1 for theS (susceptible) and R biotypes, respectively. Imazapic, sulfosulfuron, andtrifloxysulfuron reduced biomass of the S biotype greater than 60% at 8 WAT,but biomass was reduced less than 20% for the R biotype. Glufosinate,glyphosate, MSMA, and sulfentrazone reduced shoot biomass of the R biotypeby 93, 86, 97, and 45%, respectively. In laboratory experiments, thehalosulfuron concentration required to inhibit ALS activity by 50% inexcised leaf tissues was 5.8 and > 1,000 μM for the S and R biotypes,respectively. Gene sequencing of the R biotype revealed a Pro-197-Sersubstitution that confers resistance to ALS inhibitors. This is the firstreport of ALS-inhibitor resistance in annual sedge and herbicide resistancein a sedge species from a turfgrass system.